Oxidative coupling of methane over manganese oxide catalysts

Abstract

A series of Mn oxide catalysts both promoted by K and unpromoted have been prepared using high-temperature methods and investigated in the methane coupling reaction at 750 °C. Characterisation of quenched samples of the catalysts by XPS and XRD has allowed changes in the surface and bulk properties to be followed as a function of treatment conditions. The influence of injecting a single pulse of dichloromethane on the catalytic and structural properties has been investigated. Chlorine greatly enhances the selectivity of the Mn oxide catalysts for the formation of C₂ products. Structural analysis has shown that the enhanced selectivity is associated with a Mn₃O₄-like phase. This phase is unstable under reaction conditions in the absence of chlorine and the chlorine-modified phase is unstable in the absence of potassium. The relationship between the structure of the various Mn oxides and their catalytic selectivities is discussed.